The development of plastic blood collection bags facilitated the separation of donated whole blood into its various components, thereby making platelet concentrates available as a transfusion product. The separation of a single unit of donated whole blood, about 450 milliliter in USA practice, into its components is typically accomplished by use of differential sedimentation.
A typical procedure used in the United States, the citrate-phosphate dextrose-adenine (CPDA-1) system, utilizes a series of steps to separate donated blood into three components, each component having substantial therapeutic and monetary value. The procedure typically utilizes a blood collection bag which is integrally attached via tubing to at least one, and preferably two or more, satellite bags. Whole blood may be thus collected and processed as follows:
(1) The donated whole blood is collected from the donor's vein directly into the blood collection bag which contains the nutrient and anti-coagulant containing CPDA-1. PA1 (2) The blood collection bag is centrifuged together with its satellite bags, thereby concentrating the red cells as packed red cells (hereinafter PRC) in the lower portion of the blood collection bag and leaving in the upper portion of the bag a suspension of platelets in clear plasma, which is known as platelet-rich plasma (PRP). PA1 (3) The blood collection bag is transferred, with care not to disturb the interface between the supernatant PRP layer and the sedimented PRC layer, into a device known as a "plasma extractor" which comprises an opaque back plate and a transparent front plate; the two plates are hinged together at their lower ends and spring biased toward each other such that a pressure of about 90 millimeters of mercury is developed within the bag. PA1 (4) The PRP-containing satellite bag, together with another satellite bag, is then removed from the extractor and centrifuged at an elevated G force with the time and speed adjusted so as to concentrate the platelets into the lower portion of the PRP bag. When centrifugation is complete, the PRP bag contains sedimented platelets in its lower portion and clear plasma in its upper portion. PA1 (5) The PRP bag is then placed in the plasma extractor, and most of the clear plasma is expressed into the other satellite bag, leaving the PRP bag containing only sedimented platelets in about 50 ml of plasma; in a subsequent step, this platelet composition is dispersed to make PC. The PRP bag, now containing a PC product, is then detached and stored for up to five days at 20.degree.-22.degree. C., until needed for a transfusion of platelets. For use with adult patients, the platelets from 6-10 donors are, when required, pooled into a single platelet transfusion. PA1 (6) The plasma in the other satellite bag may itself be transfused into a patient, or it may be separated by complex processes into a variety of valuable products.
With the blood collection bag positioned between the two plates, a valve or seal in the tubing is opened allowing the supernatant PRP to flow into a first satellite bag. As the PRP flows out of the blood collection bag, the interface with the PRC rises. The operator closely observes the position of the interface as it rises and clamps off the connecting tube when in his judgment as much PRP has been transferred as is possible, consistent with allowing no red cells to enter the first satellite bag. This is a time consuming operation during which the operator must visually monitor the bag and judiciously and arbitrarily ascertain when to shut-off the connecting tube. The blood collection bag, now containing only PRC, may be detached and stored at 4.degree. C. until required for transfusion into a patient, or a valve or seal in the flexible tubing may be opened so that the PRC may be transferred to a satellite bag using either the pressure generated by the plasma extractor apparatus, or by placing the blood collection apparatus in a pressure cuff, or by elevation to obtain gravity flow.
Commonly used systems other than CPDA-1 include Adsol, Nutricell, and SAG-M. In these latter systems, the collection bag contains only anticoagulant, and the nutrient solution may be preplaced in a satellite bag. This nutrient solution is transferred into the PRC after the PRP has been separated from the PRC, thereby achieving a higher yield of plasma and longer storage life for the PRC.
With the passage of time and accumulation of research and clinical data, transfusion practices have changed greatly. One aspect of current practice is that whole blood is rarely administered; rather, patients needing red blood cells are given packed red cells, patients needing platelets are given platelet concentrate, and patients needing plasma are given plasma.
For this reason, the separation of blood into components has substantial therapeutic and monetary value. This is nowhere more evident than in treating the increased damage to a patient's immune system caused by the higher doses and stronger drugs now used during chemotherapy for cancer patients. These more aggressive chemotherapy protocols are directly implicated in the reduction of the platelet content of the blood to abnormally low levels; associated internal and external bleeding additionally requires more frequent transfusions of PC, and this has caused platelets to be in short supply and has put pressure on blood banks to increase platelet yield per unit of blood.
Blood bank personnel have responded to the increased need for blood components by attempting to increase PC yield in a variety of ways, including attempting to express more PRP prior to stopping flow from the blood collection bag. This has often proved to be counterproductive in that the PRP, and the PC subsequently extracted from it, are not infrequently contaminated by red cells, giving a pink or red color to the normally light yellow PC. The presence of red cells in PC is so highly undesirable that pink or red PC is frequently discarded, or subjected to recentrifugation, both of which increase operating costs.
The devices and methods of this invention alleviate the above-described problems and, in addition, provide a higher yield of superior quality PC.
In addition to the three above-listed components, whole blood contains white blood cells (known collectively as leucocytes) of various types, of which the most important are granulocytes and lymphocytes. White blood cells provide protection against bacterial and viral infection.